1. Technical Field
The present invention relates to a method and apparatus veterinary orthopedic surgical stabilization of an unstable quadruped stifle joint.
2. Related Art
The quadruped stifle is a complex and powerful joint that is stabilized by four main ligaments: the cranial cruciate, the caudal cruciate, the medial collateral and the lateral collateral. The stifle joint is further stabilized by the patella and the tendons associated therewith and the surrounding musculature. These powerful ligaments and tendons bind the femur and tibia together. Although the structure of the stifle provides one of the strongest joints of the quadruped body, as in humans, the stifle joint is also one of the most frequently injured joints. The most frequent injury occurs to the cranial cruciate ligament. The canine is the most frequently affected quadruped species. The large number of canine cranial cruciate ligament injuries has given rise to a considerable number of innovative surgical procedures and devices for attempting to replace the partially or completely torn or avulsed cranial cruciate ligament. A partially, or completely torn, stifle associated ligament or tendon typically results in serious clinical symptoms such as stifle swelling and inflammation, significant stifle pain, disuse muscular atrophy, radiographic evidence of arthritis and stifle joint instability, resulting in a significantly diminished ability to perform high level, or daily activities relating to mobility. The inevitable long term effects of a damaged and unstable quadruped stifle joint include significant meniscal and articular cartilage damage to the femur, tibia and patella. This leads to chronic pain and debilitating degenerative joint disease.
Injuries to any of the ligaments or tendons (including the cranial cruciate ligament) of the quadruped stifle typically require a major surgical intervention to repair the damage. Historically and currently these attempts at repair have involved both intra-articular and extra-articular repair procedures with varying degrees of success. More recently geometric modification of the canine stifle joint has been advocated.
As a result, several types of surgical procedures have been developed and are currently in use to attempt to mitigate the instability of the canine stifle caused by the damaged cranial cruciate ligament and/or other ligaments and tendons. Although primary cranial cruciate ligament repair would be ideal, it is unfortunately not a viable option in veterinary medicine. There are several reasons why primary repair is not viable: cranial cruciate injury in quadrupeds is rarely acute, it progresses over time and the amount of trauma that occurs to the cranial cruciate ligament is usually very severe. As a result the torn ends of the cranial cruciate ligament are not of a sufficient length to reattach successfully or have been resorbed to an extent that reattachment is not possible.
Historically intra-articular stabilization of the cranial cruciate deficient canine stifle was performed via placement of an autogenous graft, harvested either from the patella tendon or the tensor fascia lata. This method involved harvesting of the graft and then tunnelling the graft through the stifle joint and attaching so that it mimics the cranial cruciate ligament. This method has fallen out of favor due to the invasiveness of the surgical procedure required, the inherent weakness of the graft and high rate of failure of the autogenous grafting material.
All other current techniques involve extracapsular, or outside the joint repair methods. Numerous terms and techniques are utilized. One extra-capsular repair technique utilizes a synthetic nylon (commercial fishing line) or a braided polymer material. These methods both generally ultimately fail. The nylon material cycles, weakens and breaks due to movement of the stifle joint. The braided polymer material, while much stronger, either breaks, cuts through the bone, or as a result of being braided, becomes infected. These current techniques have been successful in reducing abnormal femoral/tibial movement in a sagittal plane. However, neither of these current extracapsular repair techniques permits the tibia, in relation to the femur, to internally and externally rotate as in a normal joint, nor do they permit normal compression and extension.
Another class of cranial cruciate repair surgery is the geometric modification of the quadruped stifle joint. There are currently two accepted geometric modification procedures: The tibial plateau leveling surgical osteotomy (TPLO) of the proximal tibia and tibial tuberosity advancement (TTA). The TPLO procedure involves a full thickness semi-circular osteotomy below the proximal tibia. The proximal portion of the tibial bone is then rotated counter-clockwise to decrease the tibial slope and therefore, associated cranial tibial thrust. The rotated bone is fixed in place using a specialized bone plate. The TTA procedure involves an angled, vertical cut of the tibial tuberosity. The freed portion is then advanced and fixed into place using specialized bone plating equipment. Both procedures require a very invasive surgical procedure that accomplishes its goal of decreasing cranial tibial thrust by either, transposing or rotating the cut proximal piece of tibia. The current issues surrounding these repair methods center around the requirement that, either, the caudal cruciate (TPLO) or the central patellar tendon (TTA) is required to act as the cranial cruciate ligament—a task, neither tissue was designed to do. Other issues with geometric repair methods include: the limited access of veterinarians capable of performing the procedures due to the specialized training and expensive equipment required for both the TPLO and TTA procedures. Perhaps the most alarming concern, with either of these procedures, is there is no attempt made to limit the internal rotation of the tibia relative to the femur. This is one of the primary jobs of the quadruped, cranial cruciate ligament. This is particularly important when considering that during certain parts of the stride, the quadruped stifle joint is non-weight bearing and unsupported. It is during this non-weight bearing period that internal rotation of the tibia is unrestricted greatly increasing the risk that additional quadruped stifle joint trauma can, will, and does, occur at this time.
Other ligament or tendon injuries to the quadruped stifle require different procedures to repair the damage. Many of these procedures have varying success rates.
To date no one procedure exists to stabilize an unstable, injured, or fractured quadruped stifle. Accordingly, what is needed in this art is a method of providing continuous support to the damaged, quadruped stifle during both non weight bearing and full weight bearing periods. This surgical procedure uses a surgically implanted modular quadruped stifle stabilizing device that offers continuous support, while allowing the quadruped stifle to flex, extend, internally and externally rotate, and expand and compress normally during all phases of the stride.